Heterotrophs are biological organisms that utilize energy from organic compounds for growth and reproduction. Commercial production of various carbon-based products of interest generally relies on heterotrophic organisms that ferment sugar from crop biomass such as corn or sugarcane as their energy and carbon source [Bai, 2008]. An alternative to fermentation-based bio-production is the production of carbon-based products of interest from photosynthetic organisms, such as plants, algae and cyanobacteria, that derive their energy from sunlight and their carbon from carbon dioxide to support growth [U.S. Pat. No. 7,981,647]. However, the algae-based production of carbon-based products of interest relies on the relatively inefficient process of photosynthesis to supply the reducing power needed for production of organic compounds from carbon dioxide [Larkum, 2010]. Moreover, commercial production of carbon-based products of interest using photosynthetic organisms relies on reliable and consistent exposure to light to achieve the high productivities needed for economic feasibility; hence, photobioreactor design remains a significant technical challenge [Morweiser, 2010].
Chemoautotrophs are biological organisms that utilize energy from inorganic energy sources such as molecular hydrogen, hydrogen sulfide, ammonia or ferrous iron, and carbon dioxide to produce all organic compounds necessary for growth and reproduction. Existing, naturally-occurring chemoautotrophs are poorly suited for industrial bio-processing and have therefore not demonstrated commercial viability for this purpose. Such organisms have long doubling times (minimum of approximately one hour for Thiomicrospira crunogena but generally much longer) relative to industrialized heterotrophic organisms such as Escherichia coli (twenty minutes), reflective of low total productivities. In addition, techniques for genetic manipulation (homologous recombination, transformation or transfection of nucleic acid molecules, and recombinant gene expression) are inefficient, time-consuming, laborious or non-existent.
Accordingly, the ability to endow an otherwise heterotrophic organism with chemoautotrophic capability would significantly enable more energy- and carbon-efficient production of carbon-based products of interest. Alternatively, the ability to add one or more additional or alternative pathways for chemoautotrophic capability to an autotrophic or mixotrophic organism would enhance its ability to produce carbon-based products on interest.